I. Field
This disclosure relates to satellite based wireless communication systems, in particular, a receiver for receiving a signal using a tail-biting convolutional code for error correction, transmitted on a satellite link, such as the reverse link (up-link) to a geosynchronous (GEO) satellite.
II. Background
A user terminal communicates with a gateway through a GEO satellite. The reverse link signal from the user received by the satellite is relayed to and processed by the gateway on the ground. The reverse link signal for wireless communications typically consist of the pilot signal, traffic/data signal, and the overhead signals. The pilot signal provides a reference signal known to the receiver at the gateway demodulator and is used primarily for channel estimation. The traffic signal conveys the data packets from the user application. The overhead signals are used to indicate to the gateway the information necessary to operate the forward link and reverse link.
The propagation channel distorts the reverse link signal transmitted from the user terminal by inducing an amplitude attenuation and a phase-shift. In order to demodulate and decode the data channel carried by the reverse link signal, it is necessary to estimate the amplitude and phase-shift. This is accomplished by examining the distortion induced on the reference pilot signal and is known as channel estimation. Since the pilot signal is transmitted only for the purpose of the channel estimation and since it carries no data, it is desirable to minimize the pilot power overhead as far as possible.
Typically only the pilot signal is used to estimate the propagation channel's amplitude and phase-shift, and the data is demodulated and decoded from the traffic channel using the channel estimate obtained from the pilot signal. This requires that the pilot signal be sufficiently strong for reliable channel estimation, and thus translates to higher pilot overhead. In other words, a sufficient amount of power has to be allocated to the pilot signal. However, there is a limit on the total transmit power available to the user terminal. Therefore, there is a need to develop better demodulation techniques, which requires smaller pilot signal overhead, without sacrificing demodulation performance.